The present invention relates generally to a light source apparatus, and more particularly to a light source used in an exposure apparatus for fabricating various devices including semiconductor chips such as ICs and LSIs, display devices such as liquid crystal panels, sensing devices such as magnetic heads, and image pick-up devices such as CCDs, as well as fine patterns used for micromechanics. The present invention is suitable for an exposure apparatus that uses X-ray and/or extreme ultraviolet (“EUV”) light as a light source for exposure.
Conventionally, during manufacturing, photolithography technology, a reduction projection exposure apparatus using a projection optical system to project a circuit pattern formed on a reticle (mask) onto a wafer, etc., has been employed for transferring the circuit pattern of fine semiconductor devices such as semiconductor memory and logic circuit.
The minimum critical dimension transferred by the projection exposure apparatus or resolution is proportional to the wavelength of light used for exposure and inversely proportional to the numerical aperture (“NA”) of the projection optical system. The shorter the wavelength is, the better the resolution. Thus, along with recent demands for finer semiconductor devices, shorter ultraviolet light wavelengths have been proposed—from an ultra-high pressure mercury lamp (I-line with a wavelength of approximately 365 nm) to KrF excimer laser (with a wavelength of approximately 248 nm) and ArF excimer laser (with a wavelength of approximately 193 nm).
However, lithography using ultraviolet light has limitations when it comes to satisfying the rapidly promoted fine processing of a semiconductor device. Therefore, a reduction projection optical system using extreme ultraviolet (“EUV”) light with a wavelength of 10 to 15 nm shorter than that of the ultraviolet (referred to as an “EUV exposure apparatus” hereinafter) has been developed to efficiently transfer very fine circuit patterns of 100 nm or less.
The EUV light source uses, for example, a laser plasma light source that irradiates a high-intensity pulse laser light onto a target material, such as a metal thin coating, inert gases and liquid drops, in the vacuum chamber, generates the high-temperature plasma, and uses the EUV light having a wavelength of, for example, about 13 nm.
Such EUV light source attracted people's attentions as the light source in the semiconductor fabricating as above-mentioned, and generally is not adjusted (for example, a positional correction of condenser point of EUV light etc.) in the EUV exposure apparatus after the alignment of an optical element ends. Maintaining a constant generation position of EUV light at the predetermined position have been proposed as the adjustment of the EUV light source (see, for example, Japanese Patent Application Publication No. 2000-56099). The proposal detects EUV light generated from a plasma by a pin hole camera and a CCD, and controls the generation position of EUV light by controlling a supply position of the target or a irradiation position of the pulse laser (a condenser point position of the pulse laser).
However, in prior art, because only the generation position of plasma has been detected, an actual target position is not known. Therefore, even if the condenser point position of the pulsed laser changes on the target, it is not possible to detect it. As a result, a temperature and shape etc. of plasma change, and deterioration of the exposure performance is caused by changing light intensity and light intensity distribution of EUV light used for the exposure.
The condenser point position of generated EUV light changes, as a result, because of a changing position relationship of the condenser point position of the pulse laser and the supply position of the target, and the light intensity and light intensity distribution of EUV light change similarly.